It is known in the prior art to use endovascular prostheses to treat aortic aneurysms (e.g., abdominal aortic aneurysms (“AAA”)). Such treatment includes implanting a stent, or stent-graft, within the diseased vessel to by-pass the anomaly. An aneurysm is a sac formed by the dilation of the wall of the artery, which may be congenital, but usually is caused by disease and, occasionally, by trauma. With reference to FIG. 1, sac 1 of aneurysm A is defined by dilated portions 2 of aorta AA. With the collection of blood and other embolic material in the sac 1, and being subjected to hemodynamic pressure, the aneurysm A may rupture, if untreated, causing internal bleeding.
Techniques had been developed in the prior art where diseased portions of a blood vessel, such as with an aneurysm, were ablated and replaced with a prosthetic member, such as that shown in U.S. Pat. No. 4,938,740 to Melbin. This technique, however, required open surgery. As an improvement over this technique, endovascular emplacement techniques have been developed to implant grafts and stent-grafts into a vessel from a remote puncture site, thereby obviating the need for open surgery. For example, as shown in FIG. 1, an endovascular prosthesis 3 (stent or stent-graft) is positioned to by-pass the aneurysm A with ends 4, 5 of the prosthesis being in contiguous contact with healthy portions of the aorta AA, the prosthesis 3 having been introduced endovascularly (e.g., with a catheter). Accordingly, if the aneurysm A were to rupture, blood flow through the aorta AA would be uninterrupted, and internal bleeding generally avoided. Aortic aneurysms which commonly form between the renal arteries RA and the iliac arteries IA are referred to as abdominal aortic aneurysms (“AAA”) (shown in FIG. 1). Other aneurysms are possible in the aorta, such as thoracic aortic aneurysms (“TAA”) and aortic uni-iliac (“AUI”) aneurysms.
Although considerable success has been enjoyed with stent and stent-graft performance, failures in the form of endoleaks have been noted and predominantly classified in four classes: Types I–IV. Type I failures relate to leaks between the vascular prosthesis and the vessel wall. For example, with reference to FIG. 1, a Type I failure would be blood weeping about the end 4 of the prosthesis 3 into the sac 1. Type I failures have been found to be caused by a continual expansion of the aneurysm neck (portion of the aorta AA extending cephalad or caudad from the aneurysm A). This expansion rate has been estimated to be about 1 mm/year. With the aneurysm neck expanding beyond the natural resting diameter of the prosthesis 3, passageway(s) are defined about the prosthesis 3 in communication with the aneurysm sac 1. Additionally, Type I endoleaks are also caused when circular prostheses are implanted in non-circular aortic lumens, which may be caused by irregular vessel formation and/or calcified topography of the lumen of the aorta AA.
A Type II failure involves blood flowing into the aneurysm sac through collateral vessels. Again, with reference to FIG. 1, the sac 1 may be in fluid communication with blood vessels BV, other than the aorta AA. Typically, lumbar arteries are in fluid communication (directly or indirectly) with an aneurysm sac. Since blood flow out of the sac 1 is prevented, hemodynamic pressure away from the sac 1 is not present. However, because of hemodynamic pressure within blood vessels in communication with the sac 1, blood flow, nevertheless, is directed into the sac 1 (as shown by arrows). A technique has been developed in the prior art which calls for embolizing the blood vessels BV, such as with embolus coils, thereby isolating the sac 1 from collateral blood flow. However, an additional procedure would be required for embolization.
A Type III failure is a mechanical failure, wherein a hole may be ripped into the prosthesis (e.g., excessive wear at a metal/non-metal (fabric or polymer) interface) or poor integrity exists at a connection, or connections, between modular components of a prosthesis, (e.g., extensions may be connected to the prosthesis to obtain improved securement in one or both of the iliac arteries IA.) For example, as shown in FIG. 1, a hole 6 may be torn into the prosthesis 2, or poor sealing is obtained at the connection between the prosthesis 3 and an extension 7.
A Type IV failure relates to excessive prosthesis porosity, wherein blood seeps through the prosthesis regardless of the integrity of sealing and mechanical connections.
As can be readily appreciated, even with the successful implantation of an endovascular prosthesis, failures may occur thereafter. It has been found that Type I failures may affect up to 5–10% of all implanted prostheses. Accordingly, there is a clear need for an endovascular prosthesis which can reduce the likelihood of, and ideally eliminate, Type I failures.